Compression of motor unit recruitment threshold patterns is present in the subacute phase poststroke

Area of Science:

• Neurology
• Rehabilitation Medicine
• Neuroscience

Background:

• Stroke survivors often experience persistent muscle weakness and altered neuromuscular function in the subacute phase.
• Understanding motor unit behavior is crucial for characterizing persistent deficits after stroke.
• Previous research has not fully elucidated the chronological changes in motor unit discharge patterns during stroke recovery.

Purpose of the Study:

• To characterize motor unit discharge behavior in patients with hemiplegic stroke during the subacute phase.
• To investigate changes in motor unit recruitment patterns over time in stroke survivors.
• To identify potential early indicators of persistent neuromuscular dysfunction.

Main Methods:

• Wireless surface electromyography (sEMG) was used to record motor unit activity from both affected and unaffected sides of seven subacute stroke patients.
• Participants performed isometric elbow flexion tasks, including target force-tracking and ramp tasks, at two timepoints (≥2 weeks apart).
• Two-way ANOVA was employed to analyze the interaction between timepoint and test side for recruitment threshold force (RTF).

Main Results:

• A significant interaction between timepoint and test side was observed for the recruitment threshold force (RTF) (P < 0.00).
• At the first timepoint, the RTF of the affected side was not significantly different from the contralateral side (P = 0.99).
• At the second timepoint, the RTF of the affected side was significantly lower than the contralateral side (P < 0.00), suggesting chronological worsening of recruitment abnormalities.

Conclusions:

• Motor unit recruitment patterns exhibit significant chronological alterations in the subacute phase of stroke.
• The affected limb demonstrates a progressively lower recruitment threshold force, indicating exacerbated neuromuscular abnormalities.
• Early assessment of motor unit behavior in the subacute phase can aid in detecting neuromuscular dysfunction and guiding preventive rehabilitation strategies for persistent paresis.